Variable impedance



March 1964 D. w. FLYGSTAD ETAL 3,123,793

VARIABLE IMPEDANCE Filed Oct. 8, 1962 FILELE 7 F1514- I INVENTORS 5 Dean M P2768700 FI C51 5 BY Dar/p A. Mays/2 cMAm, QA /QZT United States Patent 3,123,793 VARIABLE IMPEDANCE Dean W. Flygstad, Roseville, and David A. Meyer, Robhinsdale, Minrn, assignors, by mesne assignments, to The Telex Corporation, Tulsa, Okla, a corporation of Delaware Filed 0st. 8, 1962, Ser. No. 228,901 3 Claims. (Cl. 338-154) This invention is related to apparatus known generally as variable impedances and to contact apparatus for use therewith.

In the prior art with which this invention is concerned, a common arrangement for effecting contact with a variable impedance element such as a Wire-wound or carbon resistance or a coil winding, has been to utilize a movable wiper which is in sliding frictional and electrical contact with an impedance element. Much effort has been directed toward the improvement of sliding contact assemblies to eliminate the problems associated with mechanical wear and formation of deposits which affect the characteristics of the apparatus. These problems are greatly accentuated as further attempts have been made to miniaturize this general type of apparatus. As one example, the familiar hearing aid has been reduced from a large bulky apparatus to one which fits into an eyeglass templar member which is no larger than those found on ordinary eyeglasses. One important component of these devices is a variable resistance which is utilized as a volume or power control. The size of the present potentiometers utilized for this function is currently in the neighborhood of one-quarter inch in diameter. This is an overall dimension and it must be appreciated that the resistance element and associated contact assembly are very small. The presently available potentiometers for this purpose have been made by taking standard designs and merely making each of the parts smaller. Such potentiometers have proven to be short-lived and in some cases a life of ten thousand or less cycles of operation has proven to be an optimistic goal under actual operating conditions. This requires the user of apparatus embodying these devices to frequently replace this one important component. Furthermore, the life of such components varies greatly from one to another due to the apparent difiiculty of maintaining and achieving consistent results in the manufacture of such devices.

in the present invention, we have provided a novel and improved variable impedance apparatus which is easily and economically manufactured of low tolerance, commonly available, easily fabricated components. In the embodiment of our invention to be described below, the apparatus consists of a cylindrical housing, a rotor journaled therein, a conductive tape surrounding the rotor and having a terminal extending through the housing, an impedance element mounted on the inside periphery of the housing and having at least one terminal extending through the housing and a resilient rotatable member orbitally movable intermediate the rotor and the conductive tape. Movement of the rotor drives the rotatable elastic element around the inside of the housing and the rotatable element is of such dimension as to exert a substantial force on the conductive tape to provide current conducting, friction free, engagement of the conductive "ice tape with a small portion of the impedance element. In a manner not unlike that of a planetary transmission, there is provided in our invention an effective speed reduction between the rotor and the position of the rotatable member. By suitably proportioning the various parts, any desirable ratio may be obtained.

As may be noted from a consideration of the prior art, namely, United States Patent No. 1,677,288, issued July 17, 1928, to W. E. Newman for a Rheostat, a conductive tape has been utilized to eliminate frictional contact for the moving element in a variable resistive device. However, it is clear that our invention provides a substantial improvement and advance in the art.

It is therefore an object of this invention to provide a new and improved variable impedance device.

Another object of this invention is to provide an improved variable impedance apparatus in which an elastic rotating member is utilized to eiiect electrical contact.

A still further object of the present invention is to provide variable impedance apparatus which may be constructed of readily available materials by the use of techniques which do not require high tolerances.

It is a still further object of this invention to provide variable impedance apparatus which may be of smaller size and longer life and reliability.

These and other objects of our invention will become apparent from a consideration of the appended specification, claims and drawing, in which FlG. 1 is a bottom view of a preferred embodiment of our invention.

FIG. 2 is a sectional view taken along the section lines 2-2 in FIG. 1.

FIG. 3 is a representation of an impedance element for use in the apparatus of FIGS. 1 and 2.

FIG. 4 is a sectional view of the impedance element of FIG. 3 taken along section line 44.

FIG. 5 is a representation of a conductive tape which may be utilized in conjunction with the apparatus shown in FIGS. 1 and 2.

FIG. 6 is a sectional view of the conductive tape of FIG. 5 taken along section lines 6-6.

Referring now to FIGS. 1 and 2 of the drawing in which like reference characters have been applied to like elements, it is seen that the preferred illustrative embodiment is comprised of a hollow cylindrical housing 10 which has attached thereto for a substantial portion of the inside periphery, an impedance element 14 which is provided with a pair of radially extending terminals at each end which extend outwardly of cylindrical housing 10 through slots 31 and 32. A conductive tape 15 is mounted between portion 12 of housing It) and the body of housing 10 in a slot 13. Conductive tape 15 is of suitable dimension so that it may be in engagement with the inwardly facing surface of impedance element 14 at only one area and is positioned so as to surround rotor member 16 in the manner shown in FIG. 1. Conductive tape 15 also is provided with a terminal at one end which extends through a slot 33 in housing 10. A rotor member 16 is mounted for rotation about an axis coincident with the axis of housing 10. Rotor 16 is provided with a pair of circumferentially and radially outwardly extending portions 17 and 18 which serve to define a groove or track and is further suitably dimensioned so as to be rotatable within housing 16 when transparent lower cover member 11 is in position on the lower end of housing It) An elastic member 30 shown in the form of a sphere, is positioned intermediate the groove or track on rotor 16 and the inward facing portion of conductive tape 15. Member 39 is rotatable about an axis parallel to the axis of rotation of the rotor and the center axis of housing 19. Member 30 is shown, in FIG. 2, as being slightly deformed to clearly illustrate that it is in engagement both with the groove or track in rotor 16 to tend to retain member Cid in position and to tend to bias tape in the area of contact with member 34) into mechanical and electrical contact with impedance member 14. Rotation of rotor 16 serves to impart orbital rotation to memer 3% about the axis of said rotor to thereby variably position member 31 in accordance with the wishes of an operator. a

A suitable knob 21 for operating rotor 16 is attached to the rivet-like portion of the upper end of rotor 16 which is comprised of an axially extending portion axial ly recessed at 19, the edges of which may be rolled over to hold knob 21 as indicated by the reference charactor 29.

In operation, it may easily be seen in FIG. 1 through the transparent lower cover member 11 that rotation of member 16 serves to position member 39 in accordance with a predetermined ratio dependent upon the physical dimensions of rotor 16, member 3% and housing 10. An effective contact of tape 15 with various portions of impedance element M is possible only at the location of member 30 and is, of course, determined by the length of tape 15. In many applications, it is very desirable to effect a small variation in impedance for a fairly large rotation of a control element, such as knob 21. As noted above, this is inherent in our invention and suitable ratios may be provided for differing applications.

While member 3% is shown in the form of a spherical rubber element which has desirable, properties of elasticity, compressibility and the like, it may occur to those skilled in the art that other forms of material and shapes may be utilized in carrying out the principles of our invention. For instance, a cylindrical shape may be used and would be mounted within the apparatus so that the axis of rotation is parallel to the axis of rotation of rotor 16. The remainder of the apparatus shown in FIGS. 1 and 2 may be made of any suitable material as long as due regard is taken for providing the necessary insulation between the various elements comprising the electrical energy conducting portions of the apparatus.

In FIGS. 3 and 4 there is shown an example of an impedance element which might be utilized in connection with the apparatus shown and described in FIGS. 1 and 2. It is indicated generally by the reference numeral 40 and is comprised of a tape-like member having a pair of current conductive terminals 46 and 43 at the opposite extremities thereof and an impedance portion 54) intermediate the terminals. FIG. 4 shows, in section, an insulating base 42 to which has been applied a composition 44 which may be, for example, the carbon compound utilized in present day resistive elements. Terminals 46 and 48 may be comprised of any good conductor of electricity and may be conveniently plated on the surface of insulating base 42. One satisfactory form of insulating base was found to be Mylar tape.

In FIGS. 5 and 6 there is shown a representation of the conductive tape which is indicated generally by reference character 41 and has provided, at one end, a terminal 47 adapted for connection to other circuit elements (not shown). In FIG. 6 a cross section of conductive tape 41 is shown comprised of an insulating base 43 to which has been applied, as by plating, a conductive material 45. Insulating base 43 may be comprised of the familiar plastic Mylar and the conductive coating may be selected from the class of materials which provide good 4 electrical conduction and have suitable resistance to the formation of oxidation and the like. Terminal 47 may be comprised of a good conductive material and may conveniently be plated on the surface of the tape il over the coating 45 described above.

it is understood that suitable modifications may be made in the structure as disclosed, provided such modifications come within the spirit and scope of the appended claims. Having now therefore fully illustrated and described our invention, what We claim to be new and desire to protect by Letters Patent is:

1. A variable impedance device comprising, in combination:

(a) a hollow cylindrical housing having axially positioned apertures at each end;

([1) a spool shaped drive means rotatably journaled in said apertures;

(c) impedance means concentrically non-rotatably mounted on the inside of said housing and includin at least one terminal for connection to an electrical device;

(d) a conductive band concentrically, stationarily mounted on the inside of said housing, said band being dimensioned so that upon extension thereof toward said impedance means will result in contact therewith at only one limited area along its length, said conductive band having a terminal for connection to an electrical device; and

(e) a solid, spherical member comprised of resilient material exhibiting dielectric characteristics compressed intermediate said spool shaped drive means and said conductive band.

2. A variable impedance device comprising, in combination:

(a) a hollow cylindrical housing having axially disposed apertures at each end;

(b) drive means rotatably journaled in said apertures and having a substantial portion within said housing, said portion being of decreased diameter intermediate its ends so as to provide a track;

(0) impedance means non-rotatably mounted on the inside of said housing and including at least one terminal therefor;

(d) a conductive band surrounding said drive means and stationarily mounted within said housing intermediate said drive means and said impedance means; and

(e) a solid spherical member comprised of resilient material, said spherical member being dimensioned to be compressed intermediate the track in said drive means and said conductive band whereby rotation of said drive means variably positions said spherical member to provide adjustable electrical contact of said conductive band with said impedance means.

3. A variable impedance device comprising, in combination:

(a) a hollow cylindrical housing having coaxially positioned apertures at opposite ends thereof;

(b) drive means rotatably journaled in said apertures, said drive means extending through the ends of said housing and coaxial therewith and having a central portion positioned inside of said housing having a decreased diameter intermediate its ends;

(0) impedance means, including at least one terminal therefor, mounted on the inside concentric surface of said housing;

(d) a conductive band, including a terminal therefor, stationarily mounted inside of said housing and dimensioned to adjustably contact said impedance means at only one position at one time; and

(e) a solid resilient member of circular cross section in planes perpendicular to the axis of said drive means and dimensioned to be compressed intermediate the decreased diameter portion on said driva 1,794,154 Stsekle U Mar. 5, 1929 means and said concentric conductivs band and 1,781,959 Schefienger Nov. 18, 1930 to be pssitioned thereby. 2,135,809 Fruth Nov. 8, 1938 2,141,770 Salomon Dec. 27, 1938 References 611% in the fi1e of this patent 5 2,333,477 Duston Nov. 2, 1943 UNITED STATES PATENTS 2,467,758 Lindenblad Apr. 19, 1949 686,246 Bachmafin et a1 Nov. 12, 1901 FOREIGN PATENTS 1, 77, Nwman My 17, 1 2 34 ,035 3 m Britain y, 9, 1931 

1. A VARIABLE IMPEDANCE DEVICE COMPRISING, IN COMBINATION: (A) A HOLLOW CYLINDRICAL HOUSING HAVING AXIALLY POSITIONED APERTURES AT EACH END; (B) A SPOOL SHAPED DRIVE MEANS ROTATABLY JOURNALED IN SAID APERTURES; (C) IMPEDANCE MEANS CONCENTRICALLY NON-ROTATABLY MOUNTED ON THE INSIDE OF SAID HOUSING AND INCLUDING AT LEAST ONE TERMINAL FOR CONNECTION TO AN ELECTRICAL DEVICE; (D) A CONDUCTIVE BAND CONCENTRICALLY, STATIONARILY MOUNTED ON THE INSIDE OF SAID HOUSING, SAID BAND BEING DIMENSIONED SO THAT UPON EXTENSION THEREOF TOWARD SAID IMPEDANCE MEANS WILL RESULT IN CONTACT THEREWITH AT ONLY ONE LIMITED AREA ALONG ITS LENGTH, SAID CONDUCTIVE BAND HAVING A TERMINAL FOR CONNECTION TO AN ELECTRICAL DEVICE; AND 